1. Field of the Invention
The present invention relates to a cleaning mechanism for an image forming apparatus. More particularly, the invention relates to a cleaning mechanism for an image forming apparatus for cleaning an intermediate transfer body used upon formation of an image in an electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic apparatus or the like, a toner image is electrostatically carried on a transfer member. After transfer, a substantial amount of toner resides on a surface of a photoconductor (transfer ratio is about 80 to 90%), thereby lowering image density. On the other hand, since the toner is transferred electrostatically, it is not possible to completely prevent flying toner that may degrade the clearness of the image or contaminate the inside of the apparatus. For avoiding such defects, there has been proposed a pressure type transfer means. This type of apparatus employs appropriately 200 kg/cm2 of pressure for transferring and fixing the image. It is difficult to directly transfer the toner image on the surface of the photoconductor onto a medium to be printed and it is necessary to transfer the electrostatic latent image to a dielectric layer as an intermediate transfer body. Therefore, the apparatus can become bulky and the mechanism can be complicated. Also, when transferring the electrostatic latent image, the resolution image can be lowered.
On the other hand, there has been proposed an apparatus for developing the latent image formed on the photoconductor and transferring the developed image to an intermediate transfer body having a silicon rubber layer, and then transferring the transferred image onto a medium to be printed, which medium will be hereinafter referred to as a xe2x80x9cprinting mediumxe2x80x9d. However, such apparatus requires a large amount of heat energy for transferring and fixing the image. Also, the heat inherently elevates the temperature of the photoconductor via the intermediate transfer body, and thus the characteristics of the photoconductor may possibly be degraded.
A conventional cleaning mechanism of an image forming apparatus will be discussed in detail with reference to FIG. 6.
FIG. 6 is a side elevation showing the first prior art disclosed in Japanese Unexamined Patent Publication No. Showa 62-286082. In FIG. 6, an intermediate transfer body 503 is in belt form which is formed by coating a surface of a rigid roll of stainless or the like with a silicon rubber or the like.
The intermediate transfer body 503 is clamped between a cleaning roll 501 heated by an internal heater and a pressure roll 507 positioned in opposition to the cleaning roll 501 and is fed therethrough. Thus, a residual toner 508 on the intermediate transfer body 503 is melted by the cleaning roll 501 and deposits thereon. On the cleaning roll 501, a cleaning blade 504 which is formed with a thin plate of stainless steel or phosphor bronze, is contacted under pressure exerted by a spring 505 for removing the toner depositing on the surface thereof. The toner thus scraped is received in a waste toner box 509. On the other hand, in order to prevent the waste toner from scattering, a sheet 506 formed with a heat resistant resin film, such as polyimide film or the like, is urged onto the cleaning roll 501.
The toner on the intermediate transfer body 503 is softened to a certain extent by heat and pressure applied from the cleaning roll 501. Furthermore, since a surface free energy of the surface of metal is greater than that of the silicon rubber, softened toner is efficiently deposited on the surface of the metal of the cleaning roll 501. Furthermore, the softened toner is removed by pressure after passing through a nip portion between the cleaning roll 501 and the pressure roll 507 to be quickly hardened to be easily removed by the metallic cleaning blade 504.
One employing a cleaning belt in place of the cleaning roll 501 for removing residual ink or stains or dirt on the surface of the transfer body may possibly cause fluctuations in pressure when the cleaning belt contacts the transfer body. Also, for low absorbing speed ink, fluctuation may be caused in removal of residual ink or stains or dirt on the surface of the transfer body to form a stain on the printed product.
FIGS. 7A and 7B are a perspective view and a side elevation of the second prior art disclosed in Japanese Unexamined Patent Publication No. Heisei 04-016978, for example.
A cleaner 613 is constructed with a cleaning puff 610, a cleaning roll 622 and a take-up roll 631. A cleaning agent supplier 609 is formed with a plurality of conduits or one or more grooves to impregnate a cleaning agent stored therein into the cleaning puff 610. The impregnating method of the cleaning agent in the cleaning puff 610 may be capillary force, a pressure difference between inside and outside of the cleaning agent supplier 609, difference of concentration of the cleaning agent, heating by an electric heater, ultrasonic vibration or pumps.
The cleaning puff 610 impregnated with the cleaning agent is pressed onto a photoconductor drum 606 by the cleaning roll 622 in the vicinity of an ink absorbing portion 620. The cleaning puff 610 absorbing contaminants is taken up by the take-up roll 631. After absorbing contaminants, the cleaner 613 may rewind the almost dried cleaning puff 610 to the cleaning agent supplier 609 for reuse. Furthermore, when the same image is to be printed for a plurality of sheets simultaneously, cost may be saved by performing cleaning at a given interval or by reducing the impregnating amount of the cleaning agent.
The cleaning puff 610 may be formed with fabric paper, cloth, or plastics. However, by containing metallic or ceramic fiber, removal of static electricity or removal of solid deposits may be expected. On the other hand, the cleaning puff 610 may be formed from a porous sheet or sheet working into a particular pattern.
The cleaning agent is made of a material which may solve an ink to be used for printing. For example, in case of water soluble ink, a mixture prepared by adding a surface active agent and an antioxidant to solution of higher alcohols or glycol esters is taken as a primary component. In addition, depending upon composition of the ink, amines, ethyl""s or other esters may be used.
On the other hand, when a dispersion type ink which is prepared by dispersing a pigment into a liquid component, a solvent having the same polarity as the dispersed particle or solvent easily solving the pigment may be used.
The conventional cleaning mechanism of the image forming apparatus set forth above employs the roll form cleaning means. The conventional roll type cleaning means merely removes the residual ink on the intermediate transfer body by coating the ink component on the roll for removing the ink utilizing the fact that binding power between the ink component on the cleaning roll and the residual ink on the intermediate transfer body is greater than that between the residual ink and the surface of the intermediate transfer body. However, on the surface of the cleaning roll, impurities other than the ink, substances contained in the ink component and degrading transfer performance, paper dust from the printing paper and so forth may deposit to lower cleaning performance. On the other hand, even assuming that the substance deposited on the surface of the cleaning roll is only ink, the ink amount is not uniform over the axial direction of the roll in some images. This forms irregularities on the surface of the cleaning roll and causes a loose fit between the cleaning roll and the intermediate transfer body resulting in cleaning failure.
Therefore, it is an object of the present invention to provide a cleaning mechanism for an image forming apparatus which can assure stable cleaning performance, and constantly maintain surface conditions of an intermediate transfer body and a photoconductor to obtain satisfactory quality of printed products.
According to one aspect of the present invention, a cleaning mechanism of an image forming apparatus which transfers an ink or a toner image formed on a photoconductor to a roll form intermediate transfer body and then transfers to a printing medium for obtaining a printed product, the cleaning mechanism comprises:
a cleaning roll being contacted with the intermediate transfer body under pressure with a predetermined load and rotated with firm contact with the intermediate transfer body for removing residual ink, toner or impurity on the intermediate transfer body after a transfer process; and
a sheet member being urged onto the cleaning roll for slip contact with a predetermined load.
In the construction set forth above, a relative speed may be provided between the cleaning roll and the sheet member for slip contact to transfer ink or impurity from a surface of the cleaning roll to the sheet member.
According to another aspect of the invention, a cleaning mechanism of an image forming apparatus which transfers an ink or a toner image formed on a photoconductor to a roll form intermediate transfer body and then transfers to a printing medium for obtaining a printed product, the cleaning mechanism comprises:
a cleaning roll being contacted with the intermediate transfer body under pressure with a predetermined load and rotated with firm contact with the intermediate transfer body for removing residual ink, toner or impurity on the intermediate transfer body after a transfer process; and
a back-up roll arranged in opposition to the cleaning roll;
a sheet member being inserted between the back-up roll and the cleaning roll and slip-contacting with the cleaning roll;
a feeding roll feeding the sheet member wound thereon;
a take-up roll taking up the sheet member;
a housing receiving the back-up roll, the sheet member, the feeding roll and the take-up roll; and
an actuator connected to the housing and driving the sheet member toward and away from the cleaning roll for establishing and releasing slip contact therebetween.
A heat source, such as a halogen lamp or the like may be built into the cleaning roll for differentiating a surface temperature of the cleaning roll from a surface temperature of the intermediate transfer roll for providing large binding force with an ink for the cleaning roll.
Liquid supply means for supplying a liquid serving as a lubricant and a cleaning aiding agent to a sheet member, may be arranged within the housing. The liquid may be one of water, isopropyl alcohol and an insulative agent.
The sheet member may be in endless form.